Preparation of viscose syrups



Patented Apr. 13, 1937 2,076,595 PREPARATION OF VISCOSE SYBUPS George A. Richter, Berlin, N. E, assignor to Brown Company, Berlin, N. 11., a corporation of Maine No Drawing.

Application August 28, 1933, Serial No. 687,016

1 Claim. wi. 260-100) caustic soda and cellulose maybe put through the sub-dividing step at higher concentrations; and,

This invention relates primarily to the preparation of viscose syrups or solutions for the manufacture of artificial silk and sheet material, the sizlhgfi paper and textile 5 fabrics and various other technical uses.

In my application Serial No. 679,585, filed July 18, 1933, I have described the advantages of subdividing or reducing cellulose to a fine o pulverulent condition and then causing it to react directly in the presence of both caustic soda solution and carbon bisulphide to yield a viscose syrup of the desired strength of composition. In that application, I have further poi nted out that the caustic soda solution requisite for the if: desired objective may be of mercerizing strength, that is, the 18% caustic soda solution customarily employed for the production of a completely zanthatable soda-cellulose. The present invention is centered about a 20 modification of the general practice disclosed and claimed in that application and is aimed to facilitate the subdivision of the cellulose while at the same time leading to a preferred form of subdivided cellulose for the xanthating reaction without, however, requiring additional steps or reagents.

In accordance with the present invention, subdivision or reduction of the cellulose to a fine or pulverulent condition is performed in a wet way,

3 that is, in the presence of water. More specifically, the sub-division of the cellulose is accomplished in the presence of water containing part or all of the caustic soda designed to enter into the subsequent xanthating reaction. Such practice is advantageous in that it makes possible a reduction of cellulose pulp to the desired degree of fineness with good efliciency and with little, if any, hydration or gelatinization of the pulp fibers. Indeed, by using the caustic soda 40 necessary for the subsequent xanthating reaction as a solution of the appropriate strength and/or at the appropriate temperature, hydrating or gelatinizing action on the pulp fibers can be substantially prevented.

It is possible to produce a satisfactory viscose solution by my inventive procedure generally as follows. A suitable cellulose pulp may be subdivided in the presence of a caustic soda solution in a ball or roller mill, a beater or Jordan, or

other equivalent impact and/or cutting machine. When the ultimate objective is a viscose syrup containing about 7% caustic soda and 7% cellulose, the proportions of caustic soda, cellulose and water appropriate for such syrup may be ad- 5 mixed as raw materials. If desired, however, the

much lower than cellulose xanthate after the desired sub-division of the cellulose has been efiected, a dilution of the mass with water may be effected.

For instance, I may charge the sub-dividing machine with a 10% suspension of fiber in a 10% caustic soda solution and, after the desired sub-division of cellulose has been effected, the suspension may be diluted with water to a causticity of about 7 and carbon bisulphide added thereto to effect xanthation. In another instance, I may initially form a 7% suspension of starting cellulose in a caustic soda solution of mercerizing concentration, say, 18% or greater concentration, whereupon after the desired subdivisigin of the cellulose has been effected in such.

on, a portion of themercerizing liquor may be/separated from the sub-divided cellulose and water added to the suspension to reach the desired composition, say, caustic soda and cellulose contents of 7% each. This latter practice may be advantageous in the case of cotton or linen rags or long-fibered cellulose pulps which require extensive or prolonged sub-division before the desired fineness of cellulos e particle is reached, as

a mercerizing liquor inhibits the generation of hydrated or gelatinized cellulose even when such extensive sub-division must be accomplished.

While effecting sub-division of the cellulose, the suspension may be artificially refrigerated so as to minimize hydration or gelatinization of the cellulose especially when the caustic soda solution- -is one which does not mercerize at ordinary or Ordinarily, the lowering of room temperatures.

temperature in an aqueous suspension of cellulose fiber being beaten tends to promote a hydrating or gelatinizing action on the cellulose. In consequence of the presence of alkali during the subdivision of the fibers, however, this tendency is reversed, that is, the alkali present in the refrigerated water tends to more than ofiset the otherwise prevalent hydrating or gelatinizing action. The carbon bisulphide necessary to effect xanthation may be added while sub-division of the cellulose is going on so as to react upon and dissolve finely divided or powdered cellulose as it is progressively being generated in the ball mill, beaterengine, jordan, or other impact or cutting machine. As a rule, however, particularly when visare in view, it is prefer cose solutions of about 6% to 8% cellulose content able to add the carbon bisulphide after the desired finess of cellulose has been attained so as to avoid dimculties. Otherwise, the desired mixing action is impeded and the reduction of the unre duced cellulose fibers retarded, since the resulting viscous cellulose xantlally sub-divided to a proper degree while my,

thate acts more or less like-a lubricant and prothey can then be more easily and uniformly retecting material for the unreduced cellulose fibers. duced to the ultimate finess. desired in a wetxway.

Accordingly, the carbon bisulphide is, as already that is, in the presence of caustic soda solution- 5 indicated, preferably added at a late stage or at Insome instances, the fiber maybeinitially cut or the conclusion of the cellulose-subdividing opera-' ground in the presence of alkali-free water'and tign. Wherrhfgh cellulose content is desired in the last stage of grinding or cutting performed the finished viscose syrup, I start with a cellulose in the presence of a caustic soda solution which pulp of low solution viscosity as explained in my represses hydration to an undesirable degree such already-mentioned patent application, It m as ensues, for example, in the production of be well to again observe that thecaustic soda soluglassine papers and such as detracts from the ti h, in which subdivision or the cellulose u smoothness andrapidityof'the xanthating reacis efi'ected, may be cooled to temperature condition. If desired. the fiber used as raw material tions conducive to more or less mercerisation. m y h ve und so P u memerimflon. Ear instance, the pulp may be subdivided in a whi h case he fi e has substan ally no hycaustic soda solution of, say 6% to 7% concendrating tendencies when it is subjected to sub- I tration at temperatures in the vicinity of, say, 0 division in water. 7 O. In such instance, some mercerlzation takes A p l e mple oi procedure accordant with place at the low temperature, but when the solumy v n i n may be practiced as follows. A

tion is brought to the preferred xanthating tem- W v s yll l e fi r m y be ed as raw mercerizing activity. Inthis connection, it should t n whi h s ndertone rea ment with pcrfurther be noted that the steps of my process snsanat i n or other Solution-Woodie! may be carried out at difierent temperatures. low r gents as disclosed in in eady- Thus, asalre'ady indicateithe sub-division ofthe mentioned application. A fiber thus treated fibers may advantageously be performed at low may i ld. wh n issolved in a cup ammonium temperatures, e. g., temperatures approaching 0' solution, aviscosity approximating that of a cu- C. to minimize hydrating or gelatinizing action prammonium solution similarly prepared from and/or to promote mercerization in a solution cellulose which has been converted, into soda so which is non-mercerizing at ordinary or room cellulose and allowed to age in, accordance with temperatures. Thereupon, however, the suspenstandard viscose-making practice. The low tures,.for instance, at temperaturesappreciably mill may then be caused to rotate slowly and 40 above 30 0., in which case a ripened" viscose thus to 'grind or powder the pulp fibers progressyrup can be realized. When viscose is ripened, sively by the pounding action of the balls or rollthere is a progressive'splitting oil of water and ers. When the fibers have been reduced to parsulphur to render the cellulose, xanthate less ticles of a size passing through a fine mesh sieve. stable, that is, more precipitable'by acidic re- 7 say, one of about 200 mesh-carbonbisulphide agents, strong salt solutions, or by mere standing may be added to the suspension in the proporwhen the temperature of the heat-ripened syrup tion of three parts by weight to five parts of the is not reducedquickly and drastically. Accordcellul on a dry basis. The addition of the Y action is to take place. In any event, adequate The principles of my invention are not limited jmixing is eirected to bringthe carbon bisulphide to sub-division of. cellulose without hydration or into contact with substantially all of the, cellugelatinization, but sub-divided cellulose in a sub lose particles xanthatio is all ed to V n ow con stantially unh drated state has been found totime and the temperature of the reacting mass undergo smoother and quicker xanthation and is permitted to rise gradually to, say, 27' C. The is hence preferred. It is, however, a conperiod for complete xanthation is usually about comitant desirable result of sub-dividing cellulose three hours at the end of which time an ambermore particularly in the presence of comparacolored syrup of surprising clarity is had. Buch in a mill asby' rods; or balls tendto spin or ready described. It will. of course, be undertangle into knots or clumps, whereas, when inistood that the time required for sub-dividing the cellulose preliminary to xanthation may vary, depending upon the size of the charge and the design of the cellulose-sub-dividingmachine. Thus, the sub-division of cellulose to a particle size of finer than about 200 mesh may take from about two to four hours in the usual commercial ball mill. It will be understood that the cellulose need not necessarily be ground or pulverized to such fineness of particle size as 200 mesh, al-

though such fineness is preferable from the standpoint of ensuring a smooth, quick and substantially complete xanthation into viscose syrups of the best clarity.

It is possible to use cellulosic material or 1 pulps of a wide variety of characteristics in the practice of my invention. For'instance, one may start with chemical wood pulps, such as sulphite or kraft pulp, or wood pulps which have been refined to high alpha cellulose content, e. g.,

an alpha cellulose content of at least about 93%.

In the preparation of viscose syrups of light color intended for such purposes as the manufacture of artificial silk or sheets of regenerated cellulose, it is preferable that the cellulose pulp employed as raw material be white and of high alpha cellulose content so as to conduce to ultimates of the best appearance and physical qualities. Cellulose pulps of other than wood origin, such as cotton, manila, ramie, cotton and linen rags, etc.,

may also be employed as raw material. In the case of waste rags, reclaimed waste papers, and other impure forms of cellulose, the initial reducing step of my process in the presence of caustic soda solution may be accompanied by a considerable consumption of caustic soda in reacting upon and dissolving non-alpha cellulose components associated with the cellulose. In such case, the consumed caustic soda may be replaced .by other caustic soda at the completion of the sub-dividing operation so as to ensure a causticity in the wet, sub-divided cellulose permissive of a substantially complete xanthating reaction to produce a viscose syrup of the desired composition. In such case, too, the caustic soda solution, particularly if practically exhausted of free alkali, may be partially or completely separated as by washing from the sub-divided cellulose whereupon the sub-divided cellulose may be commingled with a caustic soda solution to produce a properly xanthatable mixture. Such latter practice is preferably adopted when considerable impurities are dissolved in the caustic soda solution present during the sub-division of the cellulose and when it is desired to attain viscose syrups of the best qualities.

The sub-division of the cellulose in thepresence of caustic soda is preferably performed in a machine whose material of construction is not affected or reacted upon by the alkali to produce undesirable contamination of the finished viscose syrup. To this end, the material of construction of the cellulose-sub-dividing machine may be chrome-steel alloy, nickel or chromium-plated steel or other metals or alloys resistant to the action of caustic soda and sulphur-containing compounds. The same holds true with the reaction vat in which the sub-divided cellulose may be xanthated after delivery from the sub-dividin machine. My invention although of particular utility in connection with the preparation of viscose syrups may be applied toother cellulose derivatives in connection with which soda-cellulose must be produced. Thus, the preparation of various cellulose ethers like ethyl and methyl cellulose ethers involve the preparation of soda-cellulose as' part and parcel ofthe etherifyingv process. In such case, the soda-cellulose mixture or combination may be producedaccordant with my invention in much the same way as the mixture is prepared for a xanthating reaction. Owing to the lack of a generic expression for-the various derivatives into which soda-cellulose may enter, in accordance with my invention. I shall adopt for convenience of designation the expression "sodacellulose derivative" as thegeneric expression in the appended claim.

The principles of the present invention may be extended to the preparation of cellulose derivatives or esters like cellulose nitrate and cellulose acetate which, rather than calling for the use of alkali-cellulose during the esterifying operation, require that the cellulose be substantially free from alkali. In such case, the cellulose pulp employed as raw material may be advantageously reduced to fine particle size in the presence of distinctly alkaline water, for instance, a caustic soda destroy its hydratability before the pulp fibers are subjected to a pulverizing operation in the presence of water, but when the reducing or pulverizing operation is performed as herein disclosed in the presence of distinctly alkaline water, it is possible to work to advantage with umnercerized cellulose pulp and in the presence of non-mercerizing alkaline solutions. In other words, when alkali is associated with the pulp fibers while they are being mechanically reduced or powdered, it is possible to repress hydration of the pulp fibers by the presence of an alkaline solution of comparatively low alkalinity and without refrigerating the solution, whereas the destruction of the hydratability of cellulose pulp by mercerization before the pulp is subjected to a pulverizing operation in the presence of water necessarily involves the more expensive expedient of using caustic soda solution of sufiiciently high strength or one artificially refrigerated to a sufficiently low temperature to exercise a mercerizing action.

I have already indicated that the cellulose xanthate solution may be formed at higher than the desired concentration and then diluted with water, or that it may be increased in causticity.

When, however, the suspension of fine cellulose particles in the caustic soda solution is such as to be incompatible with the realization of a cellulose xanthate solution ,of about 6% to 7% cellulose and about 6% to 10% caustic soda concentration, such as might be desired for spinning or casting purposes, I may add to the suspension not only carbon bisulphide to effect xanthation but such additional water, caustic soda, and fine cellulose particles as may be necessary to produce a cellulose xanthate solution of the desired cellulose and caustic soda concentration. When the suspension of fine cellulose particles has been produced in a caustic soda solution of a strength greater than that desired in the xanthating re action, for instance, a solution of about 18% or greater strength, such solution may be removed from the suspension and replaced by water so as to lower the caustic soda concentration to the de- 5 s A process which comprises mech blsulnhide may be mixed with the diluted pension to-form the solution of cellulose Iclaim:

dilidingcelluloseto a. particle size of about 200 mesh in watereontsining sumcient-caustie soda.

dissolved therein and under conditions substantie-11y to prevent hydration or gelatinintion otthe e1l1 i1ose,- pi-oportio voter. Ind caustic lodeinthe conductor the proceestoyield an aqueous suspensionofcellmoeeperticleeot emetic soda. and cellulose contents of bout 1% vv suband mixing'cerbon-bisulphide with the resulting suspension to form-e solution of cellulose xanthate. Y e

' IORGEA. RICHTER, I 

